Explosionproof lighting fixture



Aug. 3, 1937. R. B. BENJAMIN v EXPLOSIONPROOF LIGHTING FIXTURE sSheets-Sheet 1' Original Filed Jan. 25, 1933 "Aug. 3, 1937. R.B.-BENJAMIN 'EXPLOSIONPROOF LIGHTING FIXTURE original Filed Jah. 25,1935 3 Sheets-Sheet z Aug. 3, 1937. R. B. BENJAMIN 2,089,049

EXPLOSIONPROOF LIGHTING FIXTURE v Original Filed Jan. 25, 1935 sSheets-Sheet s Patented Aug. 3, 1937 UNITED STATES PATENT oFFicEApplication January 25, 1933, Serial No. 653,414 Renewed September 8,1936 6 Claims.

This invention relates to lighting fixtures and more particularly tothat type known as explosion-proof lighting fixtures; and is especiallyconstructed and adapted for use' in hazardous places where inflammableor explosive gases are present.

In this invention it is very desirable that it should be so constructedthat a widely divergent beam of light may be projected through arelatively small opening in such a manner as to illuminate large areaswith substantially uniform intensity.

It is, therefore, an object of the present invention to provide acomparatively small, compact, lighting unit in which all direct rays aredirected through a relatively small opening to provide a widelydivergent beam, and all reflected rays are caused to converge and bedirected through the opening to effect a widely divergent beam ofreinforcing rays, the combined effect of all of the rays causingsubstantially uniform intensity over a large area.

It is also an object to provide an explosionproof device which isextremely small relative to the size of lamp used and the areailluminated in which the parts are so designed and related that if thesurrounding gases leak into the fixture and become ignited the housingand associated parts will be strong enough to resist the explosionwithout damage thereto.

In a device of this type it is neither necessary nor desirable that thejoints should be airtight, but only that the leak path through thejoints be long enough between heat-conducting parts to cool the gasessufliciently as they pass out after being ignited, thereby preventingthe ignition of the gas on the outside of the fixture.

Another object is to provide a comparatively small fixture having ahousing and a light source therein with a main reflector portionpositioned about the rear of the light source, and a relatively smallopening in one side thereof through which is emitted a widely divergentbeam of intersecting rays, a second reflector portion having a diameternot substantially greater than that of the main reflector portion andpositioned forwardly thereof for reflecting rearwardly, through or nearthe light source, to the rear reflector substantially all the light rayswhich are received by it and thus redirecting the rays back through theopening in substantially the same direction as the direct rays from thelight source passing through the small opening in the housing. The smallopening is made possible by the combination of reflectors and theconstruction and arrangement of the component parts of the fixture.

The front reflector is so formed and positioned that the twice reflectedrays which are first reflected by the front reflector, and then again bythe main reflector portion, strengthen and reinforce the divergent beamof light at the outer portion of the beam so that the beam is ofprogressively "higher intensity from the center outwardly on any arcuatesurface formed with the light source as a center, whereby the lightdistribution over a fiat surface such as a floor wall or roadway is ofsubstantially uniform intensity over the entire illuminated area. Such aconstruction is unusually efficient and is suitable for lighting largeareas with a substantially uniform intensity.

A further object of the present invention is to provide a lightingfixture of the character herein described having a plurality ofsubstantially spherical reflecting surfaces and in which the focalpoints and the centers of curvature of the various reflecting portionsare so positioned relative to each other and to a light source that thereflected rays will not be concentrated at any definite conjugate focuspoint, but in which the conjugate foci will be widely distributed andtherefore there will be no hot spot on or within the material of theglass or lens or outside the fixture to cause a so-called hot spot toignite the surrounding gases.

In the past, so called explosion-proof lighting fixtures have beenprovided with a hood above the lamp and a heavy glass cylinder or globewith a spherical lower end. The glass globe was clamped to the hood andthe reflector placed above and outside the globe was necessarily oflarge diameter in order to intercept and reflect a sufficient number ofthe rays from the lamp to provide ordinary distribution. In such astructure it is'diflicult to protect the glass globe against breakageand a heavy wire guard is usually provided for that purpose. This guardintercepts a considerable number of light rays and decreases theefliciency of the fixture; also the globe is comparatively large and ina position to be easily broken and if broken the bulb is also apt tobreak and ignite the surrounding gas;

In some locations the hazard consists of dust which may easily explodeand the large external reflectors aswell as the globe of previousfixtures are subject to accumulations of dust and dirt which decreasethe efficiency and necessitate frequent cleaning and the necessaryremoval of the ua ds The fixture disclosed herein is much more compact,the distribution is more uniform, and the fixture is more efficient.Also the glass is small and protected by the housing against damage fromany angle above the horizontal, and its strength may be sufficient toobviate the necessity for a guard. The outside contour is such thataccumulation of dust is not likely to occur. The small size and shapeprevents dirt settling thereon in any large quantities.

In the fixture shown in this application, the glass is reduced to asmall size and is not easily broken but if broken is more cheaplyreplaced, and in view of the fact that all the rays, whether direct orreflected, pass through this glass, changes in the surface of the glasscan be made to vary the distribution quite materially and this canreadily be done when the glass is molded.

By employing a plurality of reflecting portions, suitably positionedrelative to a light source, substantially all the light from the lightsource may be reflected or directed through a comparatively small lensopening, while, at the same time, the diameter of the reflectors and thedimensions of the fixture may be kept within extremely small limitsrelative to the wattage of the lamp used.

As the device is of a comparatively small size and a relatively smalllight-emitting opening is required, the entire device may be muchlighter in weight and smaller in diameter than the usual constructionwherein outside reflectors are used, and a considerable saving inmanufacturing and shipping costs results. Furthermore, thecircumferential length of the seals between the various parts wherebythe device may be made explosion-proof is considerably reduced, thedanger of breakage of the lens is materially lessened, and the devicemay be more easily made completely weather-proof.

While this structure is designed primarily as an explosion-proof unitfor use in hazardous locations, it is also intended for outdoor lightingas it is weather-proof as well and is particularly suitable for use inoil fields and around gasoline filling stations.

It is evident that a great advantage is derived in constructing anexplosion-proof fixture of comparatively small size and having arelatively small lens or glass front through which substantially all thelight from the light source is projected to illuminate a large area.

It is an object of the present invention to provide a fixture of thecharacter described which will successfully withstand all of the normaland overload tests of the Underwriters Laboratories. Therefore, in thedevelopment of this lighting fixture, samples were submitted to theUnderwriters Laboratories and pipe connections were,

made to the interior ofthe housing. The fixture was then located in abomb-proof outer housing. A spark plug was inserted in the lamp housingand gasoline fumes were admitted into both housings with the lamplighted. Tests were made with various mixtures of gasoline and air, thepressures in some cases running to over pounds per square inch. Numerousexplosions were caused in the fixture and in no case was the mixtureoutside the fixture ignited, nor was the lamp broken in any instance bythe explosion within the lamp housing.

Another object is to provide a fixture of the character described whichwill be of few parts, cheap to manufacture, easy to assemble, and inwhich efilcient self-contained means is provided whereby the lens may beeasily removed or replaced and snugly fitted in position in a mannerwhereby there will be no tending to loosen other parts of the fixture orof the conduit system.

Further objects and advantages will be apparent from the specificationand the appended claims.

In the drawings:

Figure 1 is an axial cross-sectional view through an explosion-prooffixture illustrating one embodiment of my invention;

Fig. 2 is a fragmentary detail section taken on a line corresponding toline 22 of Figure 1, and illustrates the means for locking the socketagainst rotation;

Fig. 3 is a fragmentary transverse section through one side of thecasing and taken on a line corresponding to line 33 of Fig. 1;

Fig. 4 is a top plan view of the socket;

Fig. 5 is a somewhat diagrammatic view illustrating the relation of thereflectors and lens opening and the approximate light distribution;

Fig. 6 illustrates the split ring for securing the lens in its support;

Fig. 7 is a top plan View of an embodiment similar to that illustratedin Figure 1, but provided with a modified self-contained means fortightening the lens holder in the casing; and

Fig. 8 is a fragmentary side elevation of the embodiment illustrated inFig. '7 and illustrates the method of tightening the lens holder bymeans of an ordinary screw driver.

Referring to the drawings in detail, the embodiment illustratedcomprises a comparatively thick casing l of heat conducting material,preferably cast iron, having a tubular extension 2 and a lens holder 3threaded into the front end of the casing. The lens holder is also ofcomparatively thick heat conducting material similar to the housing andcomprises a ring having an inturned shoulder 4 to receive a lens orspher ical glass plate 5.

The glass is provided with a gasket-like compression washer 6,preferably of asbestos, and the washer is covered and secured by a softmetal gasket 1, which may be of thin lead, which is spun or otherwiseformed around and over the outer and upper edge of the glass. Certainunderwriters rules require glass to metal contact; therefore a thinmetal washer may, if desired, be provided between the glass andcompression washer.

The surface of the shoulder 4 on which the glass rests is usuallyaccurately finished or machined, and, as the glass may not be perfectlyflat, the compression washer and lead gasket are provided so that incase of an explosion the pressure against the glass will make the jointbetween the glass and ring such as to prevent the hot gases from readilypassing out and causing an explosion. This construction allows the useof a molded lens which is always more or less inaccurate.

The lens supporting ring 3 is provided with a lateral groove 8 arrangedto receive a resilient split ring 9 for engaging the lens and retainingit snugly in position in its support.

In the embodiment shown, threaded connections have been providedthroughout as they are well suited for cooling the hot gases which mayescape only through the long path of the threads after an explosion inthe housing.

On account of friction which might be caused between the glass-holderand the housing, means are provided for loosening or tightening theglass-holder, which means is self-contained so of the reflector portion28 is indicated at D and far as leverage is concerned, therebypreventing unscrewing the casing from the hood or :the hood from theconduit.

In the embodiment illustrated in Fig. 1, the lens supporting ring 8 isprovided with external annular gear teeth l0, and a wrench H is providedwith corresponding teeth l2 and an extension l3. The extension l3 may beinserted in a suitable opening in a lug M on the casing I to retain theteeth l2 in engagement with the corresponding teeth on the ring. Thewrench I i may then be rotated to tighten the ring snugly in the casingl, or the ring may be easily loosened thereby in order to remove thelens for cleaning or for the replacement of the lamp within the fixture.

The extension 2 of the casing l is provided with an inturned annularflange or shoulder l5 for supporting a lamp socket I6. This lamp socketis provided with an annular flange I! and a gasket l8 of lead, or othersuitable material, is spun around this flange as illustrated and in amanner to retain an asbestos compression washer [9 in position againstthe socket as .1 shown.

The usual shell and center contacts in the socket are electricallyconnected to suitable binder screws lta (Fig. 4) thus permittingconductor connections to be made without the necessity for pig-tails orcementing to prevent gases from passing through the socket and into theconduit.

The socket flange I7 is preferably provided with an angularly disposedupper surface 2|], and a hood 2i is threaded on the extension 2 and isprovided with a shoulder 22 cooperating with the inclined surface of thesocket flange and gasket thereon to thereby clamp the socket snugly inposition and provide a substantially air-tight connection.

By this construction the socket is sealed so that it is not necessary tofill back of the socket with a sealing compound as is ordinarily done tokeep gases passing from the fixture into the rest of the system, andthere are no openings past or through the socket for gases to leakthrough. They are of such a nature that they are substantially airtight. The socket is preferably of molded material and so constructedthat gases cannot pass therethrough.

A vertical groove 23 in the side of the socket is arranged to receive alug 24 on the hood 2| whereby the socket is prevented from rotationduring the insertion or removal of a lamp. A set-screw 25 in the hook 2|is arranged to lock the hood snugly in place on the housing extension 2.I

A main reflector 26 is positioned within the casing l and attachedthereto by screws 26a. The main reflector is provided with a suitableopening in alignment with the casing extension 2 to receive a lamp stem.The main reflector 26 also comprises a plurality of substantiallyspherical reflecting surfaces 2! and 28.

The construction of the device is such that a I light source will bemaintained substantially on the axis of the reflectors and substantiallyat point A (Fig. 5) relative to the reflecting surfaces and in asuitable relation to the focal points of the plurality of reflectorportions and their centers of curvature, in order to produce the desiredresults and to prevent hot spots on or in the glass or lens or on theoutside thereof.

In the embodiment illustrated, the focal point of the reflector portion21 is indicatedat B and itscenter of curvature is. at C.- Th'efocalpoint itscenter'of curvature at E and the light source A is between thecenters of curvature CE and thefocal-points B-D. By this arrangement, as

illustratedin Fig. 5, the reflected light rays from the reflectorportion 21 will cross adjacent the light source and within the casingand remote from thelens whereby they will not cause a hot spot" on thelens or outside thereof to cause an explosion outside the casing. Alsoas these reflected rays are directed through the light bulb they-will.'not cross at a definite conjugate focus .of the :rays but theywill be somewhat diffused and the crossing points will be distributedaround the axial line.

The crossing points of substantially all the reflec'ted'rays from thereflector portion 28 will be distributed in a comparatively large circleinside the casing and around the axial line as indiform distribution ofthe light beams over a large I area.

A front converging reflector 30 is secured to the reflector portion 26or adjacent thereto and provides a substantially spherical extensionthereof. This reflector may be called a zonal reflector and the centerof curvature is substantially at the light source so that substantiallyall the direct rays in the zone between the reflector 26 and the lightopening are intercepted thereby and reflected back adjacent or throughthe light source and against either the reflector portion 21 or theportion 28 whereby they are again reflected by the reflector portions 21and 28 and then pass through the lens and on substantially the samelines as the reflected rays described previously.

The reflecting surface of the zonal reflector 30 is adjacent the innersurface of the casing I and intercepts substantially all the rays whichotherwise would strike the casing. With such an arrangement ofreflectors, substantially all the light from the light source isprojected through the comparatively small lens opening and this resultis accomplished while at the same time decreasing the diameter and thelength of the casing and permitting an opening small in comparison tothe diameters of the reflectors used.

In order to provide room for the light bulb and to assist in the furtherdistribution of the light rays, the front lens 5 is preferably sphericalin shape thereby allowing sufficient distance between the lamp and thelens without increasing the length of the casing.

The particular embodiment herein shown is designed to distribute a coneof light rays with approximately a ninety degree angle but thisdistribution may be varied by suitable slight variations in thereflectors or their arrangement relative to the light source or by asuitable change in the type of lens used.

The method of attaching the lens ring to the casing I, as well as theconstruction of the casing, is a very important feature of thisinvention for the reason that while it does not provide an air tightjoint, the passage through which the gases from an explosion may escapeis small and comparatively long and all of the escaping gases must passbetween the casing and ring which are comparatively thickheat-conducting bodies.

That portion of the casing l-enclosing the main reflector 26 is concaveand conforms substantially to the contour of the reflector while athreaded cylindrical extension surrounds the zonal reflector 3B. Thisprovides fora .long threaded engagement of the glass supporting ring 3with the casing I.

'..The casing I'is preferably providedwith ribs 3 i, as indicated indetail in Fig. 3, for the purpose ofstrengthening the casing and alsoproviding a heat radiating surface.

Figs. 7 and 8 illustrate a slightly modified form ofsecuring means inwhich the casing la is provided with a plurality of outwardly extendinglugs 32, while the lens holding ring 4a is provided with a plurality ofoutwardly extending lugs 33. 1 7, .In the embodiment illustrated, thecasing la is provided with an even number of lugs equally spaced aroundthe casing, while thering 4a is provided with an odd number of lugs alsoequally spaced around the ring. By this means, one of the lugs 32 on thecasing will always be adjacent one of the lugs 33 on the ring when thering is screwed into the casing. In order to tighten the ring, it isonly necessary to insert any suitable tool such as a screw driver 34between adjacent lugs, and using the screwdriver as a lever the ringmaysbe suitably tightened.

It will be apparent to those skilled in the art thatvariousmodifications may be made without departing from the spirit andscope of this invention,and, therefore, I'desire to be limited only bythe prior art and the scopeof the appended claims.

'.What I claim and-desire to secure by Letters Patent is:

1. An explosion-proof lighting fixture of the characteridescribedcomprising a comparatively small housing having a small light openingand means for supporting a relatively large electric bulb with aconcentrated light source, said light source being positioned to directa comparatively wide angle light beam of direct rays through said'lightopening, a plurality of substantially concave reflecting surfaces remotefrom said light opening and having spaced centers of curvature forreflecting substantially one-half of all direct'rays from the lightsource through said light opening in a comparatively wide distribution,and a zonal reflecting surface positioned to reflect substantially allof the remaining direct rays against said plurality of reflectingsurfaces to be again reflected on substantially the same lines asthesingle reflected rays.

2. An explosion-proof lighting fixture of the character describedcomprising a comparatively small housing having a small light openingand means for supporting a relatively large electric bulb with aconcentrated light source, said light source being positioned to directa wide angle light beam of direct rays through said light opening,a'plurality of substantially concave refleeting surfaces remote fromsaid light opening and having spaced centers of curvature for reflectingsubstantially one-half of all direct rays from the light source throughsaid light opening in a wide angle beam, and a zonal reflecting surfacepositioned to reflect substantially all of the remaining direct raysagainst said plurality of reflecting surfaces to be again reflected onsubstantiallythe same lines as the single reflected rays, all of saidreflected rays converging to distributed crossing points within saidfixture in a manner to prevent a concentrated focus outside saidfixture.

3. An explosion-proof fixture of the character described comprising arelatively small concave casing, means for supporting a relatively largeelectric bulb in said casing, a relatively small concave reflectoraround the stem of said bulb and terminating in a plane remote from andbehind the light source, a relatively large concave reflector formingsubstantially a continuation of said small reflector and terminating ina plane adjacent to and in front of said light source, a glass platemounted in an opening in said casing and spaced from said reflectors toprovide a conical light beam through said opening from said lightsource, a zonal reflector located entirely in front of said light sourceand forming substantially a continuation of said large reflector andarranged to reflect rearwardly substantially all of the direct rays inthe zone between said large reflector and said light opening and againstsaid small and said large reflectors, said last named reflectors beingarranged to reflect and converge substantially all rays in a manner tocross inside said fixture and to prevent concentrated crossing pointsoutside.

4. An explosion-proof fixture ofthe character described comprising asubstantially gas-proof casing having a light source therein and acomparatively small glass-covered light opening therethrough, aplurality of concave reflecting surfaces in said casing for reflectingthe light from said light source forwardly and causing the rays toconverge and cross within'said casing, and a zonal reflector forreflecting rearwardly against said plurality of reflectors the directrays which otherwise would pass between said first plurality ofreflectors and said glass, said light source being located between thecenters of ourvature' of said plurality of reflectors and their focalpoints whereby all concentrated focus points will be within the fixtureand all of the crossing points of said light rays outside of saidfixture will be widely distributed.

5. A housing for an explosion-proof fixture of the character describedcomprising a concave casing having a tubular portion extending from thevertex and terminating in a socket receiving shoulder, a hood threadedon said tubular'portion and having a socket-engaging shoulder, saidshoulders being arranged to clamp a lamp socket therebetween, saidconcave portion having a cylindrical portion extending forwardlytherefrom, a lens supporting ring in threaded relation on saidcylindrical portion and having an inturned flange to receive a lens andto provide a light opening of smaller diameter than said cylindricalportion, and a lens in said ring. 6. An explosion-proof fixturecomprising a casing capable of withstanding the internal pressure due toan explosion within said casing and escaping sufiiciently to preventignition by the escaping gases and wiring terminals mounted on thesocket above the upper shoulder of the socket whereby the hot gases areprevented from reaching the space in the hood above the upper shoul- 5der of the socket.

REUBEN B. BENJAMIN.

